Well if you are getting 40 MPG, which is St rating, then you are able to go 460 miles on 14 gallons. Have you run it down to near empty to find out where you actually run out of gas. The argument is either the estimate is wrong, the gage is wrong or the fuel capacity is wrong, right? SO the tech says the light comes on with 4 gallons, and the estimate isc30 miles when the light comes on?
I do a touch better. I take 9.5 gallons at 1/4 full, and get about 415 miles. So gage seems fine, but I have never taken the gage to 10% full.
A mystery.